Trends in Serotonin Fiber Concentration and Type in the Brains of Humans in Relation to Seizure Occurrence

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Serotonin, one of the stable monoamines in the mammalian brain released at depolarized nerve terminals, is termed a neurotransmitter and has been studied for its complex relationship to epilepsy. It is thought that serotonin, which is present throughout the brain, has both excitatory and inhibitory actions through its role as a second messenger (Salgado-Commissariat and Alkadhi 1997). Animal studies done on either rats or cats have shown that as serotonin levels increase, seizure occurrence decreases (Salgado and Alkadhi 1995, Pasini 1996). However, study of human tissue is very difficult and only focuses on the morphology of the fibers and not their concentration (Trottier et al. 1996). One study has been systematic using 4 resected human epileptic neocortex samples, which found three serotonin fiber types present in the brain in differing abundance. This study did not show abnormalities in epileptic tissue (Trottier et al. 1996). In order to investigate the relationship between epilepsy and serotonin fiber concentration, we used the Trottier immunocytochemistry method with slight modifications on four epileptic patients. Sections from each patient that were recorded non-seizure (normal) and other cortex at the epileptic focus (onset) were compared for fiber concentration and type (I, II, and III). Results showed a slight trend that indicates that serotonin fiber concentrations and seizure occurrence are positively correlated in the subjects used in the experiment. In addition, results did show that fiber Type I was more prevalent in all tissue samples than both fiber Types II and III together.